EtherChannel increases the available bandwidth by carrying multiple frames over multiple links. A single Ethernet frame is always transmitted over a single link in an EtherChannel bundle.
The port-channel load-balance type global level command sets the type of load balancing. The type options include using source and destination MAC, IP addresses, and TCP and UDP ports—either a single field or both the source and destination. Because this command is global, it influences the operation of all EtherChannel bundles on a switch. The maximum number of active member links in an EtherChannel bundle is eight. A Port-channel can operate with any number of links between one and eight, inclusive.
Port-Channel Discovery and Configuration
When you are adding multiple ports to a particular Port-channel on a single switch, several configuration items must be identical-Same speed and duplex settings.
-Same operating mode (trunk, access, dynamic).
-If not trunking, same access VLAN.
-If trunking, same trunk type, allowed VLANs, and native VLAN.
-On a single switch, each port in a Port-channel must have the same STP cost per VLAN on all links in the Port-channel.
-No ports can have SPAN configured.
When a new Port-channel is created, an interface Port-channel is automatically added and it inherits the configuration of the first physical interface added to the Port-channel. If other physical interface in po differ, the physical interface will be considered as suspended from the Port-channel, and it will not become a working member until its configuration is made identical to that of the Port-channel interface.
Guidelines when configuring Port-channels:
-Do not create the interface Port-channel manually before bundling the physical ports under it. Let the switch create it and populate its configuration automatically.
-On the other hand, when removing a Port-channel, make sure to manually remove the interface Port-channel from the running config so that its configuration does not cause issues when a Port-channel with the same number is re-created later.
-Be sure to make the configuration of physical ports identical before adding them to the same Port-channel.
-If a physical port’s configuration differs from the interface Port-channel configuration, correct the physical port’s configuration first. Only then proceed to perform changes to the Port-channel interface configuration.
-A Port-channel interface can either be Layer 2 (switched) or Layer 3 (routed), depending on whether the physical bundled ports are configured as Layer 2 (switchport) or Layer 3 (no switchport). If it is necessary to change between Layer 2 and Layer 3 levels of operation, the Port-channel must be removed from configuration and re-created after the physical ports are reconfigured for the required level of operation.
-Whenever resolving an issue with err-disabled ports under a Port-channel interface, be sure to shut down both the physical interfaces and the interface Port-channel itself.
Port-channel interface inherits the MAC address of one of its physical member ports.
You can statically configure interfaces to be in a Port-channel by using the channel-group number mode on interface subcommand but this way of creating a Port-channel is strongly discouraged. If one switch considers multiple physical ports to be bundled under a single Port-channel while the neighboring switch still treats them as individual or assigns them into several bundles, permanent switching loops can occur.
Because Port-channel interfaces are treated as single ports by STP, only a single BPDU is sent for the entire Port-channel interface, regardless of how many physical links are bundled. This BPDU is also subject to the hashing function and forwarded over a single link in the entire Port-channel bundle. Assuming that the Secondary Root has the second-lowest priority in this network and that the BPDUs are forwarded over the left link toward AccessSw, the corresponding port on AccessSw is Alternate Discarding. However, the AccessSw port on the right link is not receiving any BPDUs and becomes Designated Forwarding as a result. Even though such a port sends BPDUs, they will be ignored by the Secondary Root switch because they are inferior to its own BPDUs. Hence, a permanent switching loop is created. This is also the reason why a switch shuts down all physical ports when no interface Port-channel is issued—to prevent switching loops when Port-channel configuration is being removed.
It is therefore strongly recommended to use a dynamic negotiation protocol to allow switches to negotiate the creation of a Port-channel and verify whether the links are eligible for bundling. Those protocols are the Cisco-proprietary Port Aggregation Protocol (PAgP) and the open IEEE 802.1AX (formerly 802.3ad) Link Aggregation Control Protocol (LACP). On a common Port-channel, both switches must use the same negotiation protocol; different Port-channel interfaces can use different negotiation protocols.
PAgP allows a maximum of eight links in a Port-channel. With LACP, a maximum of 16 links can be placed into a Port-channel. Out of these links, at most eight links will be active members of the Port-channel. Remaining links will be put into a so-called Standby.
LACP priority of a switch can be globally configured using the lacp system-priority command, and the priority of a port can be set up using the lacp port-priority command.
When PAgP or LACP negotiate to form a Port-channel, the messages include the exchange of key information which include system IDs of both interconnected devices, identifiers of physical ports, and aggregation groups these ports fall under.
PAgP and LACP verify only whether the links to be bundled are consistently connected to the same neighboring device and are to be bundled into the same link aggregation group. However, neither of these protocols performs checks on whether the ports on this switch and its neighbor are configured identically with respect to their operating mode, allowed VLANs, native VLAN, encapsulation, and so on.
If a Layer 2 EtherChannel is not a trunk, all ports must be assigned to the same VLAN.
QoS configuration must match and must be configured on the physical ports, not the logical one.
show etherchannel summary
show interface etherchannel //lets you verify that interface is configured with the right channel group,protocol settings
show int port-channel <number>
QoS configuration must match and must be configured on the physical ports, not the logical one.
show etherchannel summary
show interface etherchannel //lets you verify that interface is configured with the right channel group,protocol settings
show int port-channel <number>
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